1. Field of the Invention
The present invention relates generally to semiconductor switches, and more specifically, the present invention relates to semiconductor switches being switched from an off state to an on state or from an on state to an off state.
2. Background Information
In many electronic circuits using semiconductor switches, it is important to maximize circuit efficiency. In electronic circuits using semiconductor devices that are switched at high frequency, it is therefore important to minimize losses associated with turning the semiconductor switch from an off state to an on state and from an on state to an off state, often referred to as switching losses.
When a semiconductor switch is in the off state, the current flowing through the semiconductor switch is typically substantially zero and a high voltage exists across the semiconductor switch. As the semiconductor switch is switched from an off state to an on state, the current flowing through the semiconductor switch increases and the voltage drop across the semiconductor switch falls. Since power dissipation is equal to the product of voltage and current, the total energy dissipated when switching from an off state to an on state is reduced by minimizing the period of time taken to transition from an off state to an on state.
However, simply reducing the period of time taken for a semiconductor switch to switch from an off state to an on state can introduce problems in the operation of the other circuitry in the electronic circuits of which the semiconductor switch is a part. The increased rate of change of voltage, commonly referred to as dv/dt and the increased rate of change of current, commonly referred to as di/dt, increases the electrical noise created each time the semiconductor switch switches. This electrical noise can adversely affect the operation of other circuitry and it is therefore often desirable to limit the dv/dt and di/dt to keep electrical noise to acceptable levels. The need to minimize switching losses but also limit electrical noise to acceptable levels, means the design of drive circuits that provide drive signals to switch the semiconductor switch from an off state to an on state is a compromise.
Electronic circuits using semiconductor switches where it is desirable to reduce switching losses, whilst limiting dv/dt and di/dt include switching power supplies. In these switching power supplies, the drive circuits that are coupled to apply the drive signals to switch the semiconductor switch from an off state to an on state and from an on state to an off state, often form part of a power supply controller integrated circuit. The drive circuit can also comprise a power supply controller integrated circuit and discrete components, external to the integrated circuit.